1. Field of the Invention
The present invention relates to an ion current control head for flying ions from an ion generation source and controlling, by a three-layered electrode structure, ion current to be passed through a corresponding ion passage opening provided in an ion flying path.
2. Description of the Related Art
Published Examined Japanese Patent Application 61-8424 discloses an electrostatic recording system using this type of an ion current control head. FIGS. 9, 10A and 10B show an ion current control head cited from the above Japanese Patent Application. FIG. 9 is a cross-sectional view showing an arrangement of the ion current control head. The ion current head has a first matrix electrode 5c and second matrix electrode 5e. FIG. 10 A shows a planer arrangement showing segment electrode areas in the second matrix electrode 5c. An undivided continuous electrode (screen electrode) layer is arranged, as a reference electrode 5d, between the first matrix electrode 5c and the second matrix electrode 5e. The electrodes 5c, 5e and 5d provide a three-layered structure with an insulating layer 5a provided between the electrodes 5c and 5d and an pinsulating layer 5b provided between the electrodes 5d and 5e.
As shown in FIGS. 10A and 10B, the matrix electrode 5c has its own segment electrode areas arranged in a direction intersecting the segment electrode areas of the matrix electrode 5e. Openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21, 6.sub.22, . . . , . . . are provided at those intersections of the segment electrode areas of these matrix electrodes to allow the passage and control of ion current. These openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21, 6.sub.22, . . . ; . . . are arranged in a two-dimensional matrix array.
A signal corresponding to a recording image is applied across the electrode 5d and the matrix electrodes 5c and 5e to control ion current trying to pass through the control openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21, 6.sub.22, . . . ; . . . in which case the ion current is supplied from a common ion generation source. That is, with the electrode 5d as a reference, a control signal voltage is selectively applied to the first matrix electrode 5c to control whether or not the ion current is trapped in the openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21, 6.sub.22, . . . ; . . . . With the electrode 5d as the reference, a control signal voltage is selectively applied to the second matrix electrode 5e to control whether or not to pass ion current through the control openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21 , 6.sub.22, . . . ; . . . .
Thus the ion current can be controlled by the respective matrix electrodes 5c, 5e in a matrix drive mode and hence can be so done, by less number of driver circuits, relative to the larger number of control openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21 , 6.sub.22, . . . ; . . . .
In the ion current control head disclosed in the above Japanese Patent Application 61-8424 and a similar ion current control head for controlling ion current by two electrode layers of a matrix array, that electrode facing an ion generation source is comprised of a plurality of segment electrode areas 5c.sub.1, 5c.sub.2, 5c.sub.3, 5c.sub.4, . . . . In the case where a signal voltage acting to allow the ion current which comes from the ion generation source to pass through a corresponding opening and a control signal acting to allow that ion current to be suppressed relative to the other openings are supplied respectively to one segment electrode area facing the ion generation source and to the other segment areas, a potential difference between the corresponding opening and an adjacent opening exerts a greater adverse influence on an electric field of the electrode surface involved and hence the corresponding ion current to be trapped in a predetermined opening is decreased due to an adverse influence exerted by the adjacent segment electrode area acting to suppress the ion current. It is, therefore, not possible to trap an adequate amount of electric current in the corresponding opening.
This operation will be explained below with reference to FIG. 11.
Let it be assumed that ion current passes through one opening 6.sub.21 only and it is suppressed relative to the adjacent openings 6.sub.11 and 6.sub.31. Here, it is assumed that the ion current is a negative ion.
In order to trap an ion current in the opening 6.sub.21, a negative voltage of, for example, -150V is applied to the segment electrode area 5c.sub.2 with an undivided continuous electrode 5d as a reference. To the adjacent segment electrode areas 5c.sub.1 and 5c.sub.3 a positive voltage of, for example, +100V is applied, suppressing the passage of the ion current through the openings 6.sub.11 and 6.sub.31. Under this condition, an equipotential plane E1 is created in a space on the ion generation source side. FIG. 11 is a cross-sectional view showing the equipotential plane E1. The equipotential E1 provides a convex lens-like potential plane above the opening 6.sub.21 and electric lines of force created in a direction perpendicular to the convex lens-like equipotential plane are passed through the opening 6.sub.21 as narrower lines, that is, through the central area of the opening 6.sub.21.
Further, the equipotential line suffers an electric influence by the adjacent segment electrode area 5c.sub.1 and 5c.sub.3 as it goes away from the central area of the opening 6.sub.21. Viewed from these segment electrode areas 5c.sub.1, 5c.sub.2 and 5c.sub.3 throughout, a concave lens-like equipotential plane E2 is formed with the segment electrode area 5c.sub.2 as a reference. The electric lines of force spaced apart from the central area of the opening 6.sub.21 undergo an action by the concave lens-like potential plane as indicated by solid arrows in FIG. 11 and an appreciable portion of such lines of force goes toward the segment electrode areas 5c.sub.1 and 5c.sub.3 and only a portion of the lines of force near the central area of the opening 6.sub.21 is trapped in the opening 6.sub.21.
The equipotential line E3 upon the application of a voltage to the respective segment electrode areas 5c.sub.1, 5c.sub.2 and 5c.sub.3 to allow a flow of ion current though the openings 6.sub.11, 6.sub.21 and 6.sub.31, respectively, is as indicated by dotted lines in FIG. 11. In this case, the equipotential line E3 is regularly undulated with a convex lens-like wave created over each of the openings 6.sub.11, 6.sub.21 and 6.sub.31 and the ion current produces no action of displacement in any particular directions throughout a zone of the respective segment electrode areas 5c.sub.1, 5c.sub.2 and 5c.sub.3. As a result, ion current maximally trappable in the opening 6.sub.21 is more broadly directed there as indicated by the dotted arrows in FIG. 11 than the case where it is suppressed by the adjacent segment electrode areas 5c.sub.1 and 5c.sub.3 due to the suppression potential involved.
Now let it be assumed that the segment electrode areas 5c.sub.1, 5c.sub.2 and 5c.sub.3 in the matrix electrode 5c are arranged with their openings 6, . . . sequentially provided in a main scanning direction as shown in FIG. 10A and the segment electrode areas 5c.sub.1, 5c.sub.2, 5c.sub.3 . . . in the electrode 5c are sequentially selected to allow ion current to be trapped in the corresponding openings. In this case, only a narrower ion current is trapped in the opening at all times as indicated by the solid arrows in FIG. 11.
In the case where the matrix electrode 5e is such that the openings 6.sub.11, 6.sub.12, . . . ; 6.sub.21 , 6.sub.22, . . . are sequentially provided in a sub-scanning direction and an oblique direction as shown in FIG. 10B, an image signal voltage is simultaneously applied to the segment electrode areas 5c.sub.1, 5c.sub.2, 5c.sub.3 in the electrode 5c. In the case where, relative to only one opening, the segment electrode area is turned ON, the ion current is less flowed through the corresponding opening. In the case where the image signal voltage is simultaneously applied to a plurality of adjacent openings, more ion current flows through each opening.
Such an ion current control head is usually employed as a print head for printers. Depending upon the operation state in which the ion current is not properly directed, a high-speed printing head requiring more ion current cannot be realized or the printing concentration of the printer is lowered at an isolated dot type printing, such as a one-dot- or two-dot-at-a-time printing.